I. Field of the Invention
Embodiments of the present invention relate generally to vascular devices for treating certain vascular abnormalities, such as aneurysms. In particular, embodiments are directed to vascular devices including stents, grafts, and stent-grafts and methods for making vascular devices having a low profile for delivery and deployment in a patient's vasculature, such as the vessels of the thoracic area.
II. Description of the Related Art
Stents and grafts, both biological and synthetic, have been used for a large array of reparative vascular procedures, such as to treat obstructive vessels and aneurysms. An aortic aneurysm, for example, is a weakened, enlarged area in the aorta, which is the main blood vessel that carries blood from the heart to the rest of the body. Weaknesses in the aortic wall may be caused by medical conditions, such as arteriosclerosis. As blood flows through the aorta, the weak vessel wall thins over time and expands like a balloon, which can eventually burst if the vessel wall gets too thin.
Once an aortic aneurysm reaches about 5 cm in diameter, it is usually considered necessary to treat the aneurysm in an effort to prevent it from rupturing. Below 5 cm, the risk of the aneurysm rupturing is lower than the risk of conventional heart surgery in patients with normal surgical risks. The goal of therapy for aneurysms is to prevent the aorta from rupturing. Once an aortic aneurysm has ruptured, the chances of survival are low. Death may be avoided, however, if the aneurysm is detected and treated at an early stage, ideally when the aneurysm is smaller than about 5 cm, using a lower risk procedure.
Aneurysms may be treated with surgery. The surgical procedure for treating some types of aortic aneurysms involves replacing the affected portion of the aorta with a synthetic graft, which may comprise a tube made out of an elastomer or polymer material with properties that are intended to substitute the function of a normal, healthy aorta. Surgical treatment is complex, however, and may pose additional risks to the patient, especially the elderly.
More recently, instead of performing surgery to repair an aneurysm, an endovascular stent-graft may be delivered to the site of the aneurysm using elongated catheters. An endovascular stent-graft is a tube that includes a blood-impervious fabric supported by a metal mesh. It can be used to treat a variety of conditions involving blood vessels, but most commonly is used to reinforce a vessel wall at the site of an aneurysm.
To deliver a stent-graft to a target site in a patient's vasculature, typically, the surgeon will make a small incision in the patient's groin area and then insert a delivery catheter into the vasculature. The delivery catheter usually contains a collapsed, self-expanding or balloon-expandable stent-graft, which is configured to expand to approximately the normal diameter of the aorta at the location of the aneurysm or other abnormality once the stent-graft is deployed from the distal end of the delivery catheter. Over time, the stent-graft may become endothelialized, and the space between the outer wall of the stent-graft and the aneurysm should fill with clotted blood, preventing the aneurysm from growing further due to the stent-graft effectively bypassing (excluding) the aneurysm and prohibiting blood pressure and flow on the weakened segment of the patient's vasculature.
Depending on where the aneurysm is in relation to other branch vessels, different stent-graft design variations may be needed, for example, to avoid excluding blood flow through arteries that branch off from the aorta near the target site. Moreover, the stent-graft should be anchored within the lumen to reduce the incidence of migration, such as by promoting endothelialization or fixation with the vessel. Another consideration is the occurrence of endoleaks as a result of blood flowing around the stent, which may cause further weakening of the vessel wall at the site of the aneurysm.
Furthermore, the size of the delivery catheter may affect the ability of the surgeon to manipulate the catheter within the patient's vasculature. For example, when the aneurysm is located in a vessel having a small diameter and/or when the vessel diameter is reduced in size due to arteriosclerosis, larger delivery catheters may not be used or, at best, may result in trauma to the vascular tissue. Thus, the smaller the delivery catheter, the less tissue trauma should result and the easier it should be to accurately deliver the stent-graft at the proper location. Smaller delivery catheters also typically allow a physician to access smaller vessels, so as to more proactively treat aneurysms in a larger patient population.
Accordingly, there is a need for an improved vascular graft that is capable of being deployed using smaller-diameter delivery devices, is flexible for delivery through tortuous sections of vasculature, provides effective and rapid exclusion at the target site, is able to maintain its vascular position, and overcomes the shortcomings of conventional solutions.